1. Field of the Invention
The invention relates in general to a planar light source and more particularly to a light source with a mercury-heating device.
2. Description of the Related Art
After the invention of bulbs, the night life has become various and colorful. As a result of the progress of the technologies, the form and the type of the light source has become much more various. For instance, the light-emitting diode, the fluorescent lamp, tungsten filaments and the planar fluorescent lamp are nowadays popular and widely used.
The light-emitting diode can be applied on neon lamp, or electrical devices. Fluorescent lamps are widely used in indoor illumination. Tungsten filaments provide both light and heat. As for the planar fluorescent lamp, it is frequently used for providing backlight in the liquid crystal display.
Under conventionally process of producing planar fluorescent lamp, the mercury alloy is located in the planar fluorescent lamp. By means of a radio frequency heater, mercury alloy is heated and transformed into mercury vapor. Mercury vapor spreads over the planar fluorescent lamp uniformly and condenses into liquid mercury. When external electric field is applied to the planar fluorescent lamp and gas discharge occurs, mercury is excited to the excited state. When the excited mercury returns to the ground state, ultraviolet light is emitted to excite the fluorescent powder on the inner surface of the planar fluorescent lamp and visible light is generated.
In general, to transform the mercury alloy into the mercury vapor, the mercury alloy should be heated around 800° C.˜900° C. for more than 30 seconds. Consequentially, the electrical energy and time consumption is relatively essential. In addition, the cost of the radio frequency heater is high, and the process of heating using radio frequency heater is complex.